1. Field of the Invention
The present invention relates to a fuel cell system.
2. Discussion of the Background
There has been known a fuel cell installed in a fuel cell vehicle and the like, in which a membrane electrode assembly (MEA) is formed by sandwiching a solid polymer electrolyte membrane (hereinafter, called an electrolyte membrane) between an anode and a cathode from both sides, a pair of separators are arranged on both sides of the membrane electrode assembly to configure a planar unit fuel cell (hereinafter, called a unit cell), and a plurality of the unit cells are stacked so as to be a fuel cell stack. In the fuel cell, hydrogen is supplied as an anode gas (fuel gas) to the anode, air is supplied as a cathode gas (oxidant gas) to the cathode, and hydrogen ions generated by a catalytic reaction in the anode are passed through the electrolyte membrane and are moved to the cathode, thereby causing an electrochemical reaction with oxygen in the air in the cathode to generate electricity.
In the fuel cell, when the electrolyte membrane is brought into an excessively dry state (hereinafter, called a stack dry-up state), the power generation performance of the fuel cell is reduced, leading to the problem of deterioration of the electrolyte membrane. For this reason, to exhibit a desired power generation performance, the electrolyte membrane is required to be maintained in a wet state at all times.
Accordingly, Japanese Patent Application Laid-Open (JP-A) No. 2010-3480 describes a configuration in which a dew point detector is installed on an inlet side of an anode gas passage to decide whether or not a fuel cell is in the dry-up state, based on a detection value (anode inlet gas dew point) of the dew point detector.
In addition, Japanese Patent Application Laid-Open (JP-A) No. 2007-12454 discloses a technique in which when it is decided that there can be the stack dry-up, a dry-up solution process which repeats a low load operation and a high load operation to suppress temperature increase of a stack due to the continuous high load operation, and the humidified state of the fuel cell is maintained by generated water generated at the time of the high load operation.